1968 Pugliaghi. Everything clamp on even the bottom bracket gear cable guides. Pictures from TheRacingBicycle.com
In the late 1950s through the early 1970s there was a slump in bicycle sales in Europe. In the 1960s the economy was booming and although in many places the bicycle had always been the mode of transport for the working classes; many were now buying cars for the first time. At the same time the fitness craze had not yet begun; that started in the 1970s.
Racing bicycles and framebuilders were also hit by this slump and the price of a frame rose very little in that decade even though inflation did. Framebuilders had to look for ways to cut costs and one of them was to leave off all braze-ons. Building a frame without braze-ons does save a considerable amount of time and therefore labor costs. The only braze-ons seen in this era was a chainstay stop and sometimes a little stop under the down tube to prevent the gear lever clamp from sliding down the tube.
Having done that framebuilders could not tell their customers they were doing this to cut costs, hence the story that braze-ons weaken the frame. I think Cinelli started it; framebuilding was never their main source of income (Handlebar stems was.) so the price of a Cinelli frame was always high. So everyone’s thinking was if Cinelli can get away with it so can we, and they followed suit.
Do braze-ons weaken the frame? Maybe very marginally but then so does brazing the lugged joints; it is part of the framebuilding process. I have seen down tubes break right at the clamp on gear lever. Clamps require more maintenance they collect moisture under them and if they are over tightened they can dig into the tube and start a stress riser. But I feel if anyone is restoring a bike from this era they should keep the cable clamps they are authentic for the period.